So we’ve all heard the rumors and speculations. Some people report problems, and others report it working fine but at the end of the day the question still stands, “Is a Mini VBar safe on a big heli?”. With a couple small workarounds I believe it can be done safely, but if not done then it can be disastrous.
What makes a MiniV not a good idea? The power buss inside the MiniV that all the servos are powered off isn’t a very robust buss. With a full set of HV full-size servos plugged into it, the amperage requirements quickly tax the buss and a large voltage drop can occur. Not only does this make you servos perform slower, but it creates a very serious problem for Spektrum users. The little voltage regulator inside the MiniV that creates the 3.3v voltage source for the Spektrum satellites is powered form this power buss. When the source voltage for the regulator starts to get into the 4.5v and lower range there is a huge risk of those satellites losing power. This is real bad!
So how do we fix it? Well, technically we can’t. However, what we can do is help relieve some of the strain on the power buss by redirecting the current from a couple servos from ever getting there. Combine that with some sort of buffer pack/back-up unit and now we’re back in the game. Here’s a diagram on how to correctly (in my personal opinion) wire this setup with a BEC or RX pack that has two power outputs. This is how I would wire it for Spektrum or V-Control users. Futaba has a bit of an advantage because you can actually use a SBUS receiver in substitute for the Y-Cable in the diagram. The bussing on the SBUS RX’s has provided to be completely adequate to do this with and it keeps the connection points to the minimum.
The buffer pack is a really important portion of this setup. Not only does it give you a back-up power source in case of BEC failure but they help stabilize voltage ripple and keep your MiniV at a more constant voltage. This will keep your BEC happier and help dampen those large current spikes.
Hope this helps! – Nick